A variety of physical conditions involves two bodily tissue surfaces that, for treatment of the condition, need to be separated from one another and supported away from one another. Such tissue expansion may be to gain exposure to select tissue structures, to apply a therapeutic pressure to select tissues, to return tissue structures to their anatomic position and form, or in some cases to deliver a drug or growth factor to alter, influence or deter further growth of select tissues. Depending on the condition being treated, the tissue surfaces may be opposed or contiguous and may be bone, skin, soft tissue, or a combination thereof.
One particular device for treating these conditions by distracting and supporting tissue surfaces simultaneously is described in U.S. Pat. No. 6,595,998, entitled “Tissue Distraction Device”, which issued on Jul. 22, 2003 (the '998 patent). Other examples of such tissue distracting and supporting devices that are used for achieving spinal interbody fusion are described in U.S. Pat. No. 7,931,688 entitled “Expandable Interbody Fusion Device”, which issued on Apr. 26, 2011 (the '688 patent), and U.S. Pat. No. 7,967,867 entitled “Expandable Interbody Fusion Device”, which issued on Jun. 28, 2011 (the '867 patent). The '998 patent, the '688 patent and the '867 patent each discloses sequentially introducing in situ a series of elongate inserts referred to as wafers in a percutaneous approach to incrementally distract opposing vertebral bodies to stabilize the spine and correct spinal height, the wafers including features that allow adjacent wafers to interlock in multiple degrees of freedom. The '998 patent, the '688 patent and the '867 patent are assigned to the same assignee as the present invention, the disclosures of these patents being incorporated herein by reference in their entirety.
An issue that has arisen regarding such interbody fusion devices that use inserts or wafers to incrementally expand such devices is the determination of when full expansion has been achieved as a result of ligamentotaxis and no further inserts may be inserted. It is therefore desirable for a surgeon to know when a sufficient number of inserts has been introduced to stabilize the spine and correct spinal height and whether any additional inserts may be introduced. One approach addressing this issue is described in commonly assigned U.S. Pat. No. 8,828,019, entitled “Inserter for Expanding an Expandable Interbody Fusion Device”, issued on Sep. 9, 2014 (“the '019 patent”) and incorporated herein by reference in its entirety.
Accordingly, in addition to interbody fusion applications, there is a similar need for other applications that use an expandable device and inserter to insert such a device into body tissue and expand the device in situ, including the capability to determine when proper expansion of the device has been achieved and no further inserts may be introduced.